Low-frequency switching with thermostatic delay relays



H. R. CARLON July 5, 1966 LOW-FREQUENCY SWITCHING WITH THERMOSTATIC DELAY RELAYS Filed Feb. 6, 1962 w w n Qu@ w v n INVENTOR Hug/7 Gar/0n BY aw //f ATTORNEY United States Patent Office 3,259,809 Patented July 5, 1966 Army Filed Feb. 6, 1962, Ser. No. 171,544 3 Claims. (Cl. 317-132) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a system of low-frequency switching. More specifically, it relates to a system utilizing two thermal relays in a circuit, one relay being normally open `and the other relay being normally closed.

In operating an infrared Nernst Glower source, for instance, it is normal to use A.C. operation where possible. Where D.C. is more convenient, such as in the field, it is necessary to reverse the current at intervals of 'from a few seconds to several minutes to prevent deterioration of the glower. the circuit shown in the drawing.

The two relays are labeled A (115N060T) and B (ll5C60T) respectively, and are complementary type units manufactured by Amperite. The former is normally open, when cold, the latter closed. The circuit energizes relays 1 and 2, which relays are shown to actuate double pole double throw switches although any desired switching components may be used.

In the drawing, the power source is indicated as 115 v. A.C. although it may be any available type of power which will energize the filaments and relays.

When power is applied it heats the filament in tube A and simultaneously energizes relay 1. After a predetermined delay (Tl) the points in A close thereby energizing the filament in B and relay 2. For a period of time T2 both points are closed and both filaments and relays are energized. After the passage of time T2, the points in B open, deenergizing filament A and relay 1. After the passage of additional time T3, the points in A open, thereby deenergizing filament B. During time T4, both filaments are thus deactivated. After the passage of time T4, the points in B will again close thereby reenergizing filament A. The system has now completed one cycle. As shown in the drawings, there is a 90 phase shift between the energizing of the two tubes and this is clearly shown in the power diagram of the drawing. Although a wide variety of timing characteristics may be had with the cornbination, we shall for purposes of illustration assume that the points in either relay operate in exactly 60 seconds from the application of power. We shall assume further that the contacts return to their original setting 60 seconds after power is removed from the heater. Under these conditions, when power is applied, switching of either coil relay will take place every 2 minutes. Specifically, if tube A is considered, its points will remain open for 60 seconds after application of 115 A.C. to the circuit. It then closes and remains closed for 2 minutes, the first minute of which This reversal is accomplished by means of y is consumed as the heater of the other relay, which it has activated, comes up to temperature and the second minute is consumed as the original tube heater cools and returns the contacts to their starting condition. The second tube B undergoes similar operation, but out of phase with tube A. Variable resistor R is included as a compensation unit. Since no two thermal relays are precisely alike in characteristics, it is possible through adjustment of such a resistor to delay the heating and hence the operation of tube B and relay 2 so that the other relay may catch up, thus giving a true square wave output. By means of such simple inexpensive components, it is possible to secure accurately timed square wave switching.

I claim:

1. A low-frequency square wave oscillator as described, comprising rst and second input terminals, first and second complementary thermal relays, each of said relays provided with a filament and a pair of electrical contacts, the contacts of said first relay being normally opened, the contacts of said second relay being normally closed, the filament of said first relay and the contacts of said second relay series connected across said input terminals, the filament of said second relay and the contacts of said first relay series connected across said input terminals, said oscillator operative upon application of a potential to said input terminals whereupon a pulse is obtained across the filament of said first relay and the contacts of said first relay close after a predetermined period of time and thereby apply said potential across the filament of said second relay causing a pulse to be obtained across the filament of said second relay, the contacts of said second relay subsequently opening to disconnect the filament of said first relay whereupon the contacts of said first relay open and recycling occurs, and means for varying the pulse duration of at least one of said pulses.

2. The invention as set forth in claim 1 wherein said means comprises a variable resistor connected in series with the filamentof one of said relays and said potential.

3. The invention as set forth in claim 2 wherein a first electro-mechanical relay is electrically connected across the filament of said first relay, and a second electro-mechanical relay is electrically connected across the filament of said second relay.

References Cited by the Examiner UNITED STATES PATENTS 2,075,841 4/1937 Wertheimer 317-139 X 2,423,316 7/ 1947 Holmes 317-141 2,471,457 5/ 1949 Shepard 317-132 2,892,105 6/1959 Speer 317-141 X 2,958,755 11/1960 Miller 317-139 3,017,564 1/1962 Barney 317-132 X 3,059,154 10/1962 Lukianov 317-139 3,131,334 4/1964 Husband 317-132 MILTON O. HIRSHFIELD, Primary Examiner. SAMUEL BERNSTEIN, Examiner.

D. YUSKO, J. A. SILVERMAN, Assistant Examiners. 

1. A LOW-FREQUENCY SQUARE WAVE OSCILLATOR AS DESCRIBED, COMPRISING FIRST AND SECOND INPUT TERMINALS, FIRST AND SECOND COMPLEMENTARY THERMAL RELAYS, EACH OF SAID RELAYS PROVIDED WITH A FILAMENT AND A PAIR OF ELECTRICAL CONTACTS, THE CONTACTS OF FIRST RELAY BEING NORMALLY OPENED, THE CONTACTS OF SAID SECOND RELAY BEING NORMALLY CLOSED, THE FILAMENT OF SAID FIRST RELAY AND THE CONTACTS OF SAID SECOND RELAY SERIES CONNECTED ACROSS SAID INPUT TERMINALS, THE FILAMENT OF SAID SECOND RELAY AND THE CONTACTS OF SAID FIRST RELAY SERIES CONNECTED ACROSS SAID INPUT TERMINALS, SAID OSCILLATOR OPERATIVE UPON APPLICATION OF A POTENTIAL TO SAID INPUT TERMINALS WHEREUPON A PULSE IS OBTAINED ACROSS THE FILAMENT OF SAID FIRST RELAY AND THE CONTACTS OF SAID FIRST RELAY CLOSE AFTER A PREDETERMINED PERIOD OF TIME AND THEREBY APPLY SAID POTENTIAL ACROSS THE FILAMENT OF SAID SECOND RELAY CAUSING A PULSE TO BE OBTAINED ACROSS THE FILAMENT OF SAID SECOND RELAY, THE CONTACTS OF SAID SECOND RELAY SUBSEQUENTLY OPENING TO DISCONNECT THE FILAMENT OF SAID FIRST RELAY WHEREUPON THE CONTACTS OF SAID FIRST RELAY OPEN AND RECYCLING OCCURS, AND MEANS FOR VARYING THE PULSE DURATION OF AT LEAST ONE OF SAID PULSES. 